The present invention relates to stacks for fired combustion chambers and especially to an induced draft system which produces the necessary draft for a combustion chamber with a shortened stack.
In the past, it has been common to provide various types of combustion chambers for all types of uses and typically these have a stack design thereof on top of a predetermined height and shape to produce a draft up the stack generated by the heat and flow of air from the combustion chamber. Stacks have generally been required to have a predetermined height and shape in order to produce a sufficient draft to produce the necessary combustion heat in a combustion chamber. To overcome the problem with the height of the stack, it has been suggested in the past to blow air at predetermined positions in the stack to induce a draft in the stack. This has the advantage of not only reducing the height of the stack, but the increased oxygen of the stack produces a more complete combustion for many combustion chambers. Stack using draft control by the insertion of air under pressure may be seen in the King U.S. Pat. No. 3,134,345, which produces a flow of air in a circular ring directed towards the center of the stack. In the Kneass, Jr. U.S. Pat. No. 2,951,457, the air is also blown into an injector stack through an annular opening. Other U.S. patents of interest may be seen in the Campbell U.S. Pat. No. 2,584,326 for a stack draft booster and control device for combustion apparatus; while the Young U.S. Pat. No. 2,929,342 and in the Sherman U.S. Pat. No. 2,869,487 are for incinerators.
In contrast to the above patents, the present invention is directed towards an induced draft device which blows air into an enlarged annular plenum and then forces the air through a narrowed annular venturi into the stack, and which may be made of a mild steel while operating at very high temperatures by the use of a refractory lining built into the interior surface and covering the bottom portion of the annular plenum of the induced draft device.